Orthostatic headache (OH) is usually the major manifestation of spontaneous low cerebrospinal fluid (CSF) pressure, a condition being more commonly diagnosed in last two decades. [1],[2] Spontaneous intracranial hypotension (SIH) or spontaneous cerebrospinal fluid hypovolemia (SCH) is characterized by OH, low CSF pressure, and diffuse pachymeningeal enhancement on magnetic resonance imaging (MRI). The condition results from spontaneous CSF leakage from simple dural tears or meningeal diverticula. [1],[3] However, it remains underdiagnosed or misdiagnosed due to low index of suspicion. [1],[2],[4]

The syndrome has been referred to by other nomenclatures: primary intracranial hypotension, low CSF pressure headache, low CSF volume headache, hypoliquorrhoeic headache, and CSF leak headache. [1],[5] The CSF pressures, clinical manifestations, and imaging abnormalities of the syndrome may be variable. [1],[6] Epidural blood patching (EBP) is the mainstay of treatment when conservative measures fail. [1],[3]

There have been recent reports from India of SIH successfully managed conservatively, [2],[7] and only one documented report of SIH treated with EBP. [8] We report two cases of "spontaneous OHs" with normal CSF pressures but typical MRI features who responded well to EBP after conservative management had failed.

Case Reports

Case 1

A 31-year-old male presented in February 2009 with subacute onset occipital and sub-occipital moderate "pressure-like" headaches and neck pain for 2 years. The headache was precipitated by standing or walking and relieved on assuming recumbent position. There was no history of nausea, vomiting, photo-phonophobia, auras, seizures, loss of consciousness, neurological deficit, trauma, cranial/spinal surgery or fever. He had been evaluated at another hospital 1 year back where his MRI brain was normal, but CSF pressure was reported to be "low." He had been treated with EBP, following, which he had shown good recovery. Clinical examination was normal. CSF opening pressure was 80 mm water. CSF analysis was normal. MRI brain revealed thin subdural hygroma, absence of meningeal enhancement, and mild tonsillar descent [Figure 1]a-c. Contrast MRI spine and myelography, and radioisotope cisternography did not reveal an area of CSF leak. Routine laboratory parameters were normal. He was given autologous EBP with reduction in headache by 40% after 5 days followed by complete relief over days without recurrence of headache since then. Follow-up MRI showed normalization of CSF space in the posterior fossa [Figure 1]d.

A 41-year-old male presented in Oct 2009 with subacute onset, severe bifrontal throbbing headaches for 1 month. It was precipitated within 10 min of standing and relieved after few minutes in the recumbent position. He was so incapacitated with his headache that he was very fearful of getting off his bed for activities of daily living. Rest of the history, clinical examination and routine laboratory parameters were unremarkable. On clinical suspicion of SIH, MRI brain was carried out, which revealed bilateral subdural hygromas [Figure 2]a-c, diffuse meningeal enhancement [Figure 2]d,e, venous distension sign [Figure 2]c, sagging of the brain and tonsillar herniation [Figure 3]a. Contrast MRI spine did not reveal CSF leak. CSF opening pressure was 80 mm water. CSF analysis was normal. Patient did not respond to bed rest, analgesics and fluids. He responded remarkably to EBP with reduction of headache by 75% in 72 h, and was headache free after 4 weeks with no recurrence on follow-up. MRI after 3 months revealed resolution of findings [Figure 3]b-e.

SIH is characterized by low CSF pressure in the cranial cavity in the absence of head injury or lumbar puncture. [9] The estimated annual incidence of SIH is 5/100,000. Peak incidence is around age 40 with male to female ratio of 1:2. [1] OH has been defined by the International Headache Society (IHS) as headache that occurs in less than 15 min after assuming upright posture and disappears or improves in less than 30 min after resuming recumbent position. [5] OH, the signature presentation of SIH, may be of sudden or gradual onset. It is mild to incapacitating throbbing or dull pain that may be generalized or focal. Rarely, it may present as thunderclap headache. [1] Disappearance of orthostatic features, development of chronic daily headache, headache worsening with recumbency, and exertional headaches have also been reported. [1]

Mechanical factors like minor trauma or inciting event may result in dural CSF leaks. Underlying structural weakness in generalized connective tissue disorders, degenerative disc disease, and osseous spurs are rare causes. As CSF pressure decreases there is a reduction in the buoyancy of the brain resulting in sagging of the brain in the cranial cavity causing traction on its anchoring and supporting structures. [10] Traction on pain-sensitive intracranial structures causes headache and some of the associated symptoms with exaggeration of traction in upright position. [3],[6] Secondary vasodilatation of the cerebral vessels to compensate for the low CSF pressure may contribute to the vascular component of the headache by increasing brain volume.

Neck pain or stiffness, nausea, and vomiting have been described in more than 50% of patients. [1] A myriad of symptoms have been described with SIH, namely hyperacusis, echoing, tinnitus, vertigo, dizziness, blurred vision, diplopia, photophobia, unsteadiness of gait, hiccups, facial numbness, facial weakness, and dysgeusia. [1],[2] Clinical picture can sometimes mimic dementia, and sagging of the brain can cause lesions in the brainstem leading to stupor and coma. [8] Other rare manifestations include Parkinsonism More Details, ataxia, cerebellar hemorrhage, and cerebral venous thrombosis. [1],[9]

The CSF opening pressure in SIH is usually less than 60 mm water (reference range 65-195 mm water) though some patients may have consistently normal CSF opening pressures. [1] CSF is always clear and colorless with moderate lymphocytic pleocytosis, presence of red blood cells, and elevated protein. [11] CSF cytology, microbiology, and CSF glucose are always normal. [3] CSF hypovolemia rather than CSF hypotension perse has also been proposed as the underlying cause of the headache syndrome as patients with normal CSF pressures have been described who have clinical and radiographic features that are otherwise typical of OH. [12],[13] Chung etal., reported normal CSF pressure in 18% cases in their series of 30 patients. [14] Altered distribution of craniospinal elasticity due to spinal loss of CSF has been postulated as another plausible mechanism for headache. [1]

The classical MRI findings can be summarized by the acronym "Subdural fluid collections, Enhancement of the pachymeninges, Engorgement of the venous structures, Pituitary hyperemia, and Sagging of the brain." Other findings are flattening of the optic chiasm, increased antero-posterior diameter of the brainstem, and decrease in the size of cisterns and ventricles. [1] Computed tomography myelography and radioisotope cisternography are valuable tools to demonstrate and localize the CSF leak. [1]

While subdural hygromas are seen in up to 50% cases of SIH, pachymeningeal enhancement without abnormal enhancement in the depth of cortical sulci or around brainstem is the most universal MRI finding. [1],[2],[15] It is diffuse, non-nodular, involves both supratentorial and infratentorial compartments and is believed to be secondary to vascular dilatation. [1],[4],[6] It may improve or resolve with resolution of the headache. Sagging or downward displacement of the brain with effacement of prepontine cistern, flattening of pons against the clivus and descent of cerebellar tonsils mimicking Chiari 1 malformation is a very characteristic feature of SIH. [1] Brain MRI may be normal in up to 20% of patients. [1] Lack of pachymeningeal enhancement may imply inability to compensate for CSF volume loss and hence indicate less favorable prognosis. [7] First patient with subtle MRI findings had less dramatic response to EBP while the second patient with classical MRI findings had an exquisite response to EBP.

The diagnostic criteria of SIH as recommended by the IHS (7.2.3) are shown in the [Table 1]. [5] However, Chung etal., considered the presence of at least two of the following three criteria to diagnose SCH: OH, CSF pressure <60 mm water, and diffuse pachymeningeal enhancement on MRI. [14] Both our cases had normal CSF opening pressures with OH, the first case having normal CSF opening pressure on recurrence of symptoms. While, the second case had classical MRI findings, the first case had more subtle MRI features, which can be missed. In this paradigm, the CSF pressures, clinical manifestations, and imaging abnormalities of the syndrome have been hypothesized to be variables dependent on CSF volume. [6] High index of clinical suspicion without heavily relying on any one stringent diagnostic criteria is key to making a timely diagnosis of SIH or SCH.

Low CSF pressure headaches generally resolve spontaneously within 2 weeks. [11] Occasionally, it may last months, and rarely years. Majority of patients respond to conservative management based on avoidance of upright position, strict bed rest, liberal hydration, high caffeine intake, high salt intake, and addition of analgesics. [1] EBP is the mainstay of treatment when conservative management fails. [1] EBP therapy involves the infusion of 10-20 ml of autologous blood into the epidural space. Lumbar placement of EBP can be effective even when the site of CSF leakage is above the site of the blood patch or is unknown. [1] Both our cases responded well to autologous EBP despite the presence of normal CSF opening pressures. It has been hypothesized that initially the tamponade effect and later the fibrin deposition and scar formation leads to stoppage of the CSF leak and relieves the headache. Patching with fibrin glue and surgical repair of dural rent or meningeal diverticula may be required when EBP fails. [1]

Ambady etal, [7] in a series of six cases and Ramesha etal,[2] in a series of eight cases from India found benign outcome in all their cases with complete recovery on conservative management. The mean time to freedom from headache varied from less than a week to over 6 weeks in the first series, and it was 17.6 days in the second series. Our first patient had OH for 2 years with recurrence after first EBP and without much relief with conservative measures, and the second patient had debilitating OH for a month. Both our patients responded well to EBP.

Both these cases may question the utility of measuring CSF opening pressure and underscore the importance of meticulous history taking in diagnosis of OH amongst patients presenting with new daily persistent headaches particularly in patients with subtle MRI findings as in the first case. The importance of early diagnosis cannot be overemphasized as our patients even with normal CSF opening pressures responded very well to EBP.

Conclusion

SIH or SCH syndrome should form a differential of new daily persistent headaches. The condition is typified by the presence of OHs and low CSF opening pressure. Diffuse pachymeningeal enhancement and subdural hygroma are characteristic imaging features. EBP can be very rewarding in medically-refractory cases including those with normal CSF opening pressures. In order to accord greater importance to the historical component in the diagnostic criteria, we propose the nomenclature "spontaneous OHs" for this subcategory of cases.